1. Field of the Invention
The present invention relates to a member for use in a system for producing semiconductors that is provided around a susceptor for mounting a semiconductor in a chamber for producing semiconductors.
2. Related Art Statement
In a semiconductor producing system, the following two methods are known for heating a wafer when a semiconductor thin film is produced on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like:                (1) (Indirect heating system)—                    a semiconductor wafer in a chamber is heated with an infrared ray lamp provided outside the chamber; and                        (2) (Direct heating system)—                    a semiconductor wafer is mounted on a ceramic heater and heated thereon.                        
According to the indirect heating system, the thermal efficiency of the heating of the susceptor is low. It is thus difficult to elevate the temperature of the susceptor to a high temperature and to improve the temperature uniformity of the susceptor. The direct heating system is widely accepted now.
Multi-zone heaters have been known as ceramic heaters used in the direct heating system. Such a multi-zone heater has a ceramic substrate and inner and outer resistance heat generators made of metals with high melting points embedded within the substrate. Separate power supply terminals are connected to the respective heat generators so that electric power may be applied independently to the respective generators. The inner and outer heat generators may be thus independently controlled.
According to JP-A 5-326112, a resistance heat generator for a ceramic heater includes plural circuit patterns each made of a high melting point metal. The circuit patterns are so arranged that they supplement the defect portions of one another. For example, if one of the patterns has a defect portion such as a folded portion or a returning portion, another circuit pattern is overlapped on or over the defect portion of the one pattern.
For example, in a heater to be used for heating semiconductor wafers, the temperature of the heating surface of the heater needs to be uniformly controlled over the entire surface. It is required that the heater satisfies a severe specification, for example, that the temperature measured on the heating surface is within ±5° C. of the average of the whole heating surface under a use condition.
For example, a ceramic heater with an inner resistance heat generator is produced and electrical power is supplied to the heat generator so that the average temperature of the heating surface reaches a desired target value. It is now provided that the temperature over the heating surface is within a desired range after the average temperature reaches the target value. Even in this case, however, the temperature distribution on the heating surface may be substantially changed after the heater is actually fixed in a chamber. Such a change in the temperature distribution depends on various conditions, for example, when a fitting is used to fix a ceramic heater on the wall of a chamber, and the area and shape of the surface region of the heater that contacts the fitting may affect the temperature distribution. In addition to this, the temperature distribution may be affected by the thermal capacity of the fitting, the shape and thermal capacity of a chamber, thermal reflection and absorption on the inner wall surface of a chamber, and the pressures and gas flow inside and outside of a chamber.
Even when the heating surface of a ceramic heater has a desired temperature uniformity before the heater is fixed in a chamber, the temperature distribution may be out of the desired uniformity after the heater is fixed in the chamber, as explained above.
Two-zone heaters, as described above, may be effective for changing the average temperatures of the outer and inner portions of the heating surface, respectively and independently. In such a two-zone heater, however, hot spots or cold spots may be observed in only a part of the heating surface, after the two-zone ceramic heater is fixed in a chamber. The two-zone control system is not effective for reducing such cold and hot spots observed in only a small part of the heating surface.
The inventors also considered a system including a ceramic heater divided into many zones and having separate resistance heat generators provided in each corresponding with each of the zones. The electric power to the heating elements is independently controlled. When a cold spot is observed in one of the zones of the heating surface, it is effective to increase the electric power supplied to the heat generator corresponding to the zone with the observed cold spot. Such an increased electric power to the zone improves the heat generation so that the cold spot may be reduced or cancelled.
The inventors have investigated this idea, however, and finally found that the control is also ineffective for reducing the temperature distribution. That is, the temperature of each zone of the heating surface is influenced by the heat generation right under the zone, as well as the heat generation by other heat generators provided right under another zones, respectively. The temperature distribution on the heating surface is determined by many factors including heat generated from each heat generator, the shape, dimension and thermal capacity of the ceramic substrate, and the temperature, pressure and gas flow around the substrate. Such factors may affect each other. It is possible to reduce or cancel a cold spot by increasing the electric power supplied to a heat generator corresponding with the zone with the observed cold spot. In this case, however, the heat generated from the heating element right under the cold spot is transmitted to the adjacent zones, so that the total balance of heat generation and transfer in the substrate and the temperature distribution on the heating surface may be changed. Such a change in the balance of the heat generation and transfer may generate a hot spot on the heating surface or increase the average temperature of the surface. When the average temperature of the heating surface is increased, it is necessary to reduce the electric power supplied to other heat generators provided for other zones. Such a reduction of the electric power supplied to other heat generators may induce other cold spots on the heating surface. The difference between the maximum and minimum temperatures on the heating surface may be thus increased in many cases by canceling one cold spot.
An object of the present invention is to provide a method of heating a semiconductor on a susceptor in a chamber, in which the temperature distribution on the susceptor can be reduced even when the target temperature of the susceptor is high.